152 



PHAEOPHYCEAE 



degenerate and the centre becomes filled with a gas. The fronds are 

 simple or branched and bear small superficial cells with sporangia 

 and mucilage hairs scattered over the surface in sori. The pluri- 

 locular and unilocular sporangia occur on the same or on different 

 plants, the sori with unilocular sporangia containing sterile para- 

 physes in addition. The principal interest of this type is centred 

 around its life history which has been studied by several workers in 



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 jdanl 



Zx 



9 





t.x 



c<. 



'l^LiintuLe <- 



DICTY05IPH0N 



^CK 



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X. 



Ect.bUrxt 







5motkd.liu£> — 





etrel/loTierm. — > Yt — >o< 





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Zx. 



Fig. 105. Diagram of life cycles of Dictyosiphon foeniculaceus and Asperococcus 

 hullo sus. 



considerable detail. In A. compressus the life cycle is simple, the 

 zooids from the unilocular sporangia germinating directly into a 

 protonemal phase that later turns into small plantules; these can 

 reproduce themselves successively by means of zoospores from 

 both pluri- and unilocular sporangia until the advent of favourable 

 conditions enables the development of the macroscopic phase to 

 take place once m.ore. There is no evidence of either meiosis or of 

 gametic fusion. In A.fistulosus it would appear that the life cycle is 

 dependent upon the behaviour of the zooids from the unilocular 



